In particular in the field of microlithography, apart from the use of components designed to have the highest possible precision it is, among other things, desirable during operation to set the position and orientation of optical modules of the imaging device, and thus for example the modules with optical elements such as lenses, mirrors and gratings but also the masks and substrates used, as accurately as possible within specified setpoint values, or to stabilise such components in a specified position or geometry, in order to achieve a correspondingly high imaging quality (wherein in the sense of the present disclosure the term optical module can mean both optical elements alone as well as assemblies of such optical elements and further components, such as for example holder parts, etc.).
To this end support structures are often used in which a plurality of support elements cooperate in a parallel kinematic fashion in order to position and orient the optical element in all six degrees of freedom. A typical example of such parallel kinematics is so-called hexapods, in which six support elements (usually in three pairings, or so-called bipods) position and orient the optical element in relation to a larger support unit in the form of a ring shaped retainer. Often for the support elements simple, leaf-spring-like elements are used here, as for example are known from WO 02/16993 A1 (Shibazaki), the full disclosure of which is incorporated herein by reference.
These configurations often have the disadvantage that perpendicular to the plane of the retainer they are comparatively high-rise so that the manipulators in a configuration of the optical system with optical elements close together generally have to be nested with each other, in order to guarantee the desired distance between the optical elements. This can bring along the further disadvantage that the optical elements can only be fitted to be rotated with respect to one another to a limited extent (for example around the optical axis of the system), so that it is frequently not possible to combine two or more optical elements in such a way that imaging errors (for example caused by deformation of the optics) of the optical elements can mutually compensate each other.
From EP 1 632 799 A1 (Shibazaki), the full disclosure of which is incorporated herein by reference, a hexapod structure with a low-rise in the direction of the optical axis is known, in which the optical element is supported by six support members, which in each case at both ends are joined to the adjacent components by a flexure acting in the form of a ball joint. Here adjustment of the optical element takes place in that the articulation point of the support member assigned to the external supporting structure is displaced tangentially to the circumferential direction of the optical element, so that the articulation point of the supporting body assigned to the optical element is inter alia displaced in the direction of the optical axis of the optical element.
As a result of the articulation used in the form of a ball-joint, while the desired adjusting kinematics are achieved in a small area, there is nevertheless a problem that the two flexures can have only a comparatively low cross-sectional area so that under just static loading, but above all under dynamic loading (with high accelerations), relatively high stresses in the bending elements can arise. The consequence of this is that, firstly, the lifetime of the manipulators of the optical elements can be limited or only comparatively low accelerations may be permitted and thus (for a specified adjusting range) only relatively small adjusting movements can be made. In view of the continuing trend towards increasing travel with greater adjusting ranges, this can be extremely disadvantageous.
A further disadvantage of this configuration can be that in the region of the ball joints possible tilting motions can lead to a falsification of the position of the articulation point assigned to the optical element in the direction of the optical axis and thus to reduced positioning accuracy.